Thermal insulating composite

Abstract

Process to manufacture an insulating laminate composite structure comprising the following steps: a. provide a laminate composite structure precursor (7) comprising the following layers on a first layer (1) made of a fiber fabric in the following order; - a second layer (2) made of a material having a thickness below 0.3 mm, said material having a melting point higher than 200°C and said layer having an air porosity below than 5 cm3 / sec measured according to ASTM 737, -a third layer (3) made of microporous layer comprising metal oxide having a density between 100-450 g / m3 - a fourth layer (4) comprising a mica paper having a thickness below 0.3 mm, - optionally a fifth layer (5) is present, said layer is made of fiber fabric, said laminate composite structure precursor being sewed with a heat resistant yarn (6); b. impregnate the layer or the layers made of a fabric with a matrix precursor material before or after shaping the laminate composite structure precursor, c. press and cure the laminate composite structure.

Description

[0001] Thermal insulating composite

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a process to produce thermal insulating laminate composite structure which withstands a temperature up to 1200°C, to a thermal insulating composite structure and to a thermal insulation composite structure precursor.

[0004] BACKGROUND OF THE INVENTION

[0005] The present invention refers mainly to the transportation industry, including aerospace, automotive, and marine sectors, where there is a continual demand for lightweight materials that offer fire resistance, flame penetration resistance, avoiding flame spread and thin thermal insulation properties.

[0006] Composite material are widely used in applications requiring high strength-to-weight ratios. It consists of reinforcing fibers, such as carbon fibers, fiberglass, basalt fibers or aramid fibers, which are impregnated with a matrix material, usually a thermosetting resin like epoxy. The main drawback of these composites material is their behaviour regarding heat, specially for the epoxy resins. The composite materials do not withstand high temperature because of the resin used. The composite material starts to degrade above the decomposition temperature of the resin used and will start burning or having combustion at higher temperature. Decomposition temperatures start around 200°C for epoxy resins till 400°C for polyimide . The composite material looses indeed their mechanical integrity although the use of fire retardant to improve their thermal behaviour. Some specific resins such polyimide can withstand high temperature but for a short time while the mechanical strength at ambient temperature is much lower than epoxy resins and the price much higher. Another issue of the use of composite material is the risk of auto ignition of the resins at temperature below 400°C.

[0007] The purpose of the invention is multiple:

[0008] 1. Thin Thermal insulation of the composite with improved acoustic when exposed to temperature below decomposition temperature of the binder or the matrix used to make the composite.

[0009] 2. Protect the structural side of the composites when exposed to temperature above decomposition temperature of the binder or the matrix used to make the composite.

[0010] 3. Allow composite to resist in case of fire by protecting the composite from high heat, avoid degradation of the binder or the matrix in the composite to maintain its integrity or mechanical strength and to avoid flame spread and burn-through on protected while maintaining a total thickness of the composite preferably below 55 mm, down to 2.5 mm. SUMMARY OF THE INVENTION

[0011] The first object of the invention is to provide a process to produce a thermal insulating laminate composite structure comprising the following steps: a. provide a laminate composite structure precursor comprising the following layers on a first layer made of an fiber fabric in the following order;

[0012] - a second layer made of a material having a thickness below 0.3 mm, said material having a melting point higher than 200°C and said layer having an air porosity below than 5 cm3 / sec measured according to ASTM 737,

[0013] -a third layer made of microporous layer comprising metal oxide having a density between 100-450 g / m3

[0014] - a fourth layer comprising a mica paper having a thickness below 0.3 mm,

[0015] - optionally a fifth layer is present, said layer is made of an fiber fabric, said laminate composite structure precursor being sewed with a heat resistant yarn; b. impregnate the layer or the layers made of a fabric with a matrix precursor material before or after shaping the laminate composite structure precursor, c. press and cure the laminate composite structure.

[0016] The first layer is made of fiber fabric. The fibers may be selected among glass fibers, Carbon fibers, basalt fibers, aramid fibers , silica fibers or quartz fibers. The first layer is the cold face of the composite structure meaning that it should not be exposed to flame or high temperature.

[0017] The second layer is made of a material having a thickness below 0.3 mm, said material having a melting point higher than 200°C and said layer having a porosity below than 5 cm3 / sec measured according to ASTM D-737-18. It is obviously understood that it is the second layer which has a thickness below 0.3 mm. This low porosity layer prevents the liquid resin or matrix precursor needed to impregnate the fabric from penetrating the microporous layer. In preferred embodiments the second layer comprises a mica paper. The mica paper is preferably a mica reinforced with heat resistant flexible binder. Such binder may be silicone binder . The mica paper reinforced or not may also be laminated onto a glass fibre fabric which improved the handling of the mica paper. The weight of the mica layer may vary from 25 to 300 g / m^ and preferably from 30 to 130 g / m^ . The advantage of the mica paper- at the opposite of the mica sheet- is that the mica paper is flexible which easier to handle. The mica paper provides a flame protection. Its low thickness also allows to be sewn with other layers. US2003170418 describes common mica papers. When looking for enhanced insulation and reduced thickness, a layer comprising an aerogel polyimide is used. In that case, the layer should be in the "cold side" of the structure. Indeed this polyimide layer would not withstand temperature higher than 500°C and would be then destroyed. In another embodiment, the second layer comprises a mica paper and an aerogel polyimide film which is inserted between the mica layer and the fiber fabric.

[0018] The third layer is made of a microporous layer which is known per se, for instance from GB1580909 and US6936326. The microporous layer comprises a porous metal oxides material compacted to consolidate the material into a handleable form and in addition thereto an opacifier and optionally a reinforcing fiber. In ASTM C168, microporous insulation is defined as "material in the form of compacted powder or fibres with an average interconnecting pore size comparable or below the mean free path of air molecules at standard atmospheric pressure. Microporous insulation may contain opacifiers to reduce the amount of radiant heat transmitted". Microporous materials are characterized by a very low thermal conductivity of less than 40 mW / m.K and even significantly lower. The microporous layer does not fill a honeycomb structure.

[0019] The density of the microporous layer is in the range of 100- 450 Kg / m^, for example between 100 to 200 Kg / m3, or between 200 to 300 Kg / m^or between 300 to 450 depending the insulation and the thickness targeted. The microporous layer has a thermal conductivity between 23-36 mW / mK at 400°C.

[0020] The microporous layer has a thickness between 0.5 and 50 mm. In some embodiments the thickness of the microporous layer may be for example between 0.5 to 10 mm, or between 1 to 5 mm, or between 1 and 3 mm. In other embodiments the thickness of the microporous layer is for example between 10 and 50 mm, or between 15 and 29 mm, or between 30 and 50 mm.

[0021] The microporous layer comprises 30 to 90 wt% of finely divided metal oxide, 5-60 wt % of an opacifier material, 1 to 10 % of inorganic fibres and 0 to 50% of filler. The microporous layer may be free of aerogel and of xonotlite.

[0022] The metal oxide is chosen among -silica, alumina and preferably is pyrogenic silica or pyrogenic Alumina or mixed oxide or pyrogenic . The surface areas of the metal oxides are ranging from 50-400 m2 / g.

[0023] The opacifier is selected from titanium dioxide, iron titanium oxide, zirconium silicate and iron oxide and mixtures thereof, in an amount of 12-40%, preferably 15-40%. Inorganic fibers are also present between 1 to 10%. These fibers can be of E, S, R glass in composition, silica fibers as well as alumina fibers or ceramic fibers and body soluble fibers by composition (alkaline oxide and alkaline earth oxide contents > 18% with temperature limit over 1000°C).

[0024] Mixed fibers are also possible as well as small addition of organic or cellulosic fibers (0-3%). The fibers diameter can be 0.2-12 microns with of 3-12 mm in length. Preferably, 0.3-7 microns in diameter and 3-6 mm in length.

[0025] In a further implementation, the optional filler in the microporous powder composition is a material chosen from the group of water glass, precipitated and amorphous silica, calcium silicate, perlite, calcium sulphate, including gypsum materials, aluminum phosphates, borides of aluminum, titanium, zirconium, calcium, silicides such as calcium silicide and calcium aluminum silicide, basic oxides such as magnesium oxide, calcium oxide and barium oxide oxide in an amount of 0-30%, preferably higher than 5 wt%.

[0026] The fourth layer comprises a mica paper as described here above, the mica paper has a thickness below 0.3mm, preferably below 0.15 mm. The thickness of the third layer is preferably between 0.025 and 0.3 mm.

[0027] Preferably, a fifth layer made of a fiber fabric as described here above is present in the composite structure. The fiber fabric is intended to be impregnated with a matrix precursor such as a resin. When a fifth layer is used , the microporous layer is encapsulated in a composite structure. Because the fifth layer is stitched to the insulating core, it reinforces the cohesive strength of the composite and allows the addition of further prepregs.

[0028] All the layers are sewn together using a heat-resistant yarn having a diameter below 0.5 mm, preferably 0.2-0.4 mm and a tex below 250 g / lOOOm. The Tex is preferably between 200 and 220 g / lOOOm. When the temperature is higher than 400°C, the tex and the diameter are essential such as the conductivity of the yarn and then the diameter of the hole created by melting of the yarn do not jeopardize the global insulation of the composite structure.

[0029] The heat resistant yarn is preferably made of E glass or quartz or silica and most preferably stainless steel reinforced aramid (sold under the name of Kevlar) if the temperature of use is higher than 500°C.

[0030] All the layers are sewn together. The resulting stiches forms lines in at least on direction, the parallel stiches lines are separated from a maximum of 1 cm. In a preferred embodiment the resulting stiches form rectangular area. In some embodiments, the areas are in the range of 25 x 25 mm or 30 x 30 mm or 50 x 50 mm. The composite precursor is then ready to be shaped and be impregnated (or vice- versa) with a matrix precursor material.

[0031] The laminate precursor is then pressed and cured. The pressure can be applied using a variety of methods, including vacuum bagging, autoclave, or compression molding, resin transfer molding hydraulic presses.

[0032] Hot pressing is usually then operated at a temperature higher than 60°C, depending on the matrix to be cured.

[0033] In a preferred embodiment, the matrix to cure is a polymer matrix due to their ease of processing, low cost and good mechanical properties.

[0034] Common thermosetting resins which can be used are epoxy resins, phenolic resins, polyester resins , vinyl ester polyester, polyacrylate, polyimide, bismaleimide resin, cyanate ester. Epoxy resins are preferred because of the cured matrix provide high mechanical resistance and low prices.

[0035] An alternative to the use of fabric which are impregnated with a matrix material precursor is to use pre-impregnated (pre-preg) layers. Caution must be taken as the prepreg need to be stored in a refrigerated conditions to prevent premature curing.

[0036] The mechanical strength of the structure precursor can be enhanced by adding to the first layer or the fifth layer, at least one prepreg comprising an inorganic or organic fabric impregnated with a resin. This is done after the impregnation of the inorganic fabric. The resulting structure is then shaped and hot pressed. Another embodiment is to insert between the prepreg and the first layer a honeycomb. This will increase even more the mechanical strength of the composite structure and improve acoustic insulation.

[0037] A second aspect of the invention relates to a thermal Insulating Laminate composite structure comprising the following layers on a first layer made of a resin impregnated fabric skin in the following order:

[0038] - a second layer made of a material having a thickness below 0.3 mm, said material having a melting point higher than 200°C and said layer having an air porosity below than 5 cm^ / sec measured according to ASTM 737,

[0039] -a third layer made of microporous layer comprising metal oxide having a density between 100-450 g / m3,

[0040] - a fourth layer comprising a mica paper having a thickness below 0.3 mm,

[0041] - optionally a fifth layer is present, said layer is made of resin impregnated fabric skin, said laminate composite structure precursor being sewed with a heat resistant yarn; This thermal insulating laminate composite structure is the product obtained by the process described here above. All the features described here above apply for the composite structure.

[0042] According to some embodiments, the thermal insulating laminate composite has a total thickness between 2.5 and 55 mm, preferably between 3 to 15 mm, most preferably between 3 to 8 mm.

[0043] The resin impregnated fabric skin is a fiber reinforced polymer layer (FRP).

[0044] The heat resistant yarn of the laminate composite structure precursor is made of glass, quartz preferably stainless steel reinforced aramid.

[0045] The second layer comprises a polyimide aerogel or a mica paper.

[0046] When the microporous layer is sandwiched between two mica papers, the presence of an aerogel polyimide layer between the second layer made of mica and the resin impregnated fabric skin increases significantly the thermal insulation without increasing significantly (less than 1 mm) the total thickness of the composite.

[0047] A third aspect of the invention provides a thermal insulating laminate composite structure precursor for the formation of a thermal insulating laminate composite structure comprising the following layers on a first layer made of a pre-impregnated fabric or of a fiber fabric to be impregnated with a resin in the following order

[0048] - a second layer made of a material having a thickness below 0.3 mm, said material having a melting point higher than 200°C and said layer having an air porosity below than 5 cm3 / sec measured according to ASTM 737,

[0049] -a third layer made of microporous layer comprising metal oxide having a density between 100-450 g / m3

[0050] - a fourth layer comprising a mica paper having a thickness below 0.3 mm,

[0051] - optionally a fifth layer is present, said layer is made of impregnated fabric skin or on a fiber fabric to be impregnated with a resin said laminate composite structure precursor being sewed with a heat resistant yarn;

[0052] All the features described here above about the layers apply for the thermal composite structure precursor.

[0053] A preferred embodiment is a thermal insulating laminate composite structure precursor wherein the second layer of the laminate composite structure precursor is a mica paper or a layer comprises polyimide aerogel.

[0054] A fourth aspect of the invention is the use of a thermal insulating laminate composite structure as described here above having two external main surfaces, to provide a structure having a total thickness less than 5mm wherein one external surface remains below 420 °C after 75 minutes while the other external surface is exposed to the temperature raising according to ISO 834-2019.

[0055] BRIEF DESCRIPTION OF THE FIGURES

[0056] For a fuller understanding of the nature of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings in which:

[0057] Figure 1(a) shows a cross view of a thermal insulation laminate composite structure precursor according to the present invention.

[0058] Figure 1(b) shows a top view of a thermal insulation laminate composite structure precursor according to the present invention.

[0059] Figure 2 illustrates the test firing of Examples 1 and 2. The temperature of the oven is represented by a dot line T. The temperature on the cold side of Example 1 (EXI) is represented by the continuous curve, which represents the maximum temperature of the temperatures measured by 5 thermocouples attached to the cold side of Example 1. Similarly, the temperature on the cold side of Example 2 (EX2) is represented by the dash curve which represents the maximum temperature of the temperatures measured by 5 thermocouples attached to the cold side of Example 2.

[0060] DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0061] The present invention will be described with respect to particular embodiments.

[0062] Example 1

[0063] A composite structure having a total thickness of 3.7 mm was made of a layer of 1.5 mm of microporous layer comprising silica oxide having a density of 400 Kg / m^ was sandwiched between two reinforced mica papers having thickness of 0.125 mm. This core of the three layers was then sandwiched between two glass fabric having each a thickness of 0.9 mm. A polyimide aerogel of 0.16 mm was inserted between one mica paper and the impregnated resin layer. The layers are then sewn with a stainless steel reinforced Kevlar having a diameter of 0.2mm and a tex of 215 mm. The microporous layer was composed of 59% of pyrogenic silica , 38% of rutile and 3 % of silica fibers.

[0064] The impregnation of the glass fabric was made once the layers were sewed. Glass fabric were impregnated with an epoxy resin then pressed at 120°C for 90 minutes.

[0065] The fire test according to ISO 834- 2019 was conducted as following; The 30 x 30 cm sample was imbedded in a wall closing an oven of dimension 1.2 m x 1.2 m x 0.6 m: burners were used to increase the temperature in the oven. The temperature in the oven was then raised from 20 °C according to ISO 834 from 20 °C up to 980°C after 75minutes for partition application. 5 thermocouples were attached to the cold side of the tested sample.

[0066] Example 2

[0067] A composite structure having a total thickness of 4.9 mm was made of a layer of 2.8 mm of microporous layer comprising silica oxide having a density of 400 Kg / m^ was sandwiched between two mica papers having thickness of 0.125 mm. This core of the three layers was then sandwiched between two glass fabric having each a thickness of 0.9 mm. The structure is then sewn with a stainless steel reinforced Kevlar having a diameter of 0.2mm and a tex of 215 mm. The microporous layer was composed of 59% of pyrogenic silica , 38% of rutile and 3 % of silica fibers.

[0068] The impregnation of the glass fabric was made once the layers were sewed.

[0069] Same procedure than for example 1 was applied.

[0070] Results Table 1

[0071] The increase of the temperature in the oven was set to follow the thermal curve of ISO834-2019. However, after 6 minutes the temperature in the oven increases suddenly because of the resin combustion on the hot side. Therefore, furnaces burners were turnoff such as the upper limit of the Iso temperature curve was not crossed. The burners were then switched on again after few minutes.

[0072] After 5 minutes the temperature of the oven was just above 600°C while the temperature of the cold face was below 200 °C for both samples. The temperature at the cold side increases slowly to reach a plateau around 400°C while the temperature of the oven was at 980°C after 75 min.

[0073] The integrity of the structure remains after the test.

[0074] Example 1: total thickness 3.7 mm; aerogel film and 1.5 mm of microporous layer 400Kg / m^

[0075] Example 2: total thickness 4.9 mm: 3 mm of microporous layer 400 Kg / m^

Claims

CLAIMS1. Process to manufacture an insulating laminate composite structure comprising the following steps: a. provide a laminate composite structure precursor (7) comprising the following layers on a first layer (1) made of a fiber fabric in the following order;- a second layer (2) made of a material having a thickness below 0.3 mm, said material having a melting point higher than 200°C and said layer having an air porosity below than 5 cm^ / sec measured according to ASTM 737,-a third layer (3) made of microporous layer comprising metal oxide having a density between 100-450 g / m^- a fourth layer (4) comprising a mica paper having a thickness below 0.3 mm,- optionally a fifth layer (5) is present, said layer is made of fiber fabric, said laminate composite structure precursor being sewed with a heat resistant yarn (6); b. impregnate the layer or the layers made of a fabric with a matrix precursor material before or after shaping the laminate composite structure precursor, c. press and cure the laminate composite structure.

2. Process according to the previous claim wherein the second layer of the laminate composite structure precursor comprises a mica paper or a polyimide aerogel.

3. Process according to any one of the previous claims wherein the heat resistant yarn is made of glass, quartz , silica , basalt preferably stainless steel reinforced aramid.

4. Process according to any one of the previous claims wherein the matrix precursor material is thermoset resin selected among a phenolic resin , a polyester , polyimide , bismaleimide resin , cyanate ester and preferably an epoxy resin.

5. Process according to any one of the previous claims wherein the mica paper is a reinforced mica layer laid down on a glass fiber fabric.

6. Process according to any one of the previous claims wherein the fabric is a pre-impregnated fabric with a resin and wherein the step b consists of shaping of the laminate composite structure precursor.

7. Process according to any one of the previous claims wherein at least one prepreg comprising a fabric impregnated with a resin is added on the first layer of the laminate composite structure precursor after the impregnation of the inorganic fabric.

8. Thermal Insulating Laminate composite structure comprising the following layers on a first layer made of a resin impregnated fabric skin in the following order:- a second layer made of a material having a thickness below 0.3 mm, said material having a melting point higher than 200°C and said layer having an air porosity below than 5 cm3 / sec measured according to ASTM 737,-a third layer made of microporous layer comprising metal oxide having a density between 100-450 g / m3- a fourth layer comprising a mica paper having a thickness below 0.3 mm,- optionally a fifth layer is present, said layer is made of resin impregnated fabric skin said laminate composite structure precursor being sewed with a heat resistant yarn;9. Thermal Insulating Laminate composite according the previous claim wherein the laminate composite structure have total thickness 2.5 to 55 mm, preferably 3 to 15 mm, most preferably between 3 to 8 mm.

10. Thermal Insulating Laminate composite according to any one of claims 8 to 9 wherein the resin is a thermoset resin chosen among a phenolic resin , a polyester , polyimide , bismaleimide resin , cyanate ester and preferably an epoxy resin.

11. Thermal Insulating Laminate composite according to to one of claims 8 to lOwherein the heat resistant yarn of the laminate composite structure precursor is made of glass, quartz preferably stainless steel reinforced aramid.

12. Thermal Insulating Laminate composite according to anyone of the claims 8 to 11 wherein the second layer comprises a poiyimide aerogel .

13. Thermal Insulating Laminate composite according to anyone of the claims 8 to 11 wherein the second layer comprises mica paper.

14. Thermal Insulating Laminate composite according the previous claim wherein a aerogel polyimide layer is present between the second layer made of mica and the resin impregnated fabric skin .

15. Thermal Insulating Laminate composite structure precursor (7) for the formation of a thermal insulating laminate composite structure comprising the following layers on a first layer made of a pre-impregnated fabric or of a fabric to be impregnated with a resin in the following order- a second layer made of a material having a thickness below 0.3 mm, said material having a melting point higher than 200°C and said layer having an air porosity below than 5 cm3 / sec measured according to ASTM 737,-a third layer made of microporous layer comprising metal oxide having a density between 100-450 g / m3,- a fourth layer comprising a mica paper having a thickness below 0.3 mm,- optionally a fifth layer is present, said layer is made of impregnated fabric skin on a fiber fabric to be impregnated with a resin said laminate composite structure precursor being sewed with a heat resistant yarn; 16. Use of a thermal insulating laminate composite structure as described here according to any one of the claims 8 to 14 to provide a composite structure having two external main surfaces and a total thickness less than 5mm wherein one external surface remains below 420 °C after 75 minutes while the other external surface is exposed to the temperature raising according to ISO 834-2019.

Images